OBSERVATIONS ON THE MATURATION PROCESSES. 33 



The circumpolar bodies have been so named because they are 

 grouped around the poles of the spindle (figs. 13, 14). Their origin is 

 not known beyond the fact that they come into existence gradually at 

 the spindle poles. They are variously shaped (figs. 13a, 136, 14, 14a, 

 15), no one form having predominance over others. Some have irreg- 

 ular forms or are roughly spherical, others are pear-shaped, still others 

 disk-like. In ordinary plasma stains they are very inconspicuous, 

 apparently being composed of a homogeneous substance somewhat 

 denser than the surrounding cytoplasm. In phosphotungstic-acid hsema- 

 toxylin, on the contrary, they become deep blue, like the chromosomes, 

 from which they are distinguishable only by their forms. They appar- 

 ently have no connection with the spindle fibers (figs. 13a, 136, 14a), 

 and after the chromosomes have reached the ends of the spindle they 

 fade away (plate 3, fig. 16) and disappear altogether (plate 4, fig. 18). 



The clear region around the spindle is often visible in sections as a 

 faint, broad zone before the circumpolar bodies appear (figs. 11 and 12), 

 and it often persists for a short time after they have vanished (figs. 16 

 and 18). When most conspicuous it is comparatively narrow. It ap- 

 pears more homogeneous than the surrounding cytoplasm by reason of 

 its being less granular; but at no time is it quite free from granules. 



5. Position and Orientation of first Maturation spindle. 



The depth at which the spindles lie is variable. Whether the fully 

 formed spindle remains at first in the position which was occupied by the 

 germinative vesicle when its membrane vanished is undecided. At all 

 events, before the time when the chromosomes divide, the spindles may 

 be found at different depths. When the polar cell is about to be cut off 

 the spindle comes to lie near the surface of the egg, assumably in the 

 region of the animal pole. The axis of the spindle may be parallel, 

 oblique, or perpendicular to a tangent to the surface of the egg at the 

 point nearest the spindle. These positions are not characteristic of 

 particular stages, but may be found at any epoch in the maturation. 

 The perpendicular position is least often met with, the oblique at vari- 

 ous angles, and the parallel positions are the most frequent. It seems 

 quite possible that the spindle maintains its original orientation when 

 it approaches the surface to divide. At least, it is certainly true that 

 the perpendicular position is not requisite for the formation of the polar 

 cell (see p. 34), for of ten spindles in the stages shown in figs. 15, 16, and 

 17, only one was perpendicular, the others being either parallel or some- 

 what oblique. The perpendicular one was in a stage corresponding to 

 that illustrated by fig. 15. In nearly all examples of the stage shown in 

 fig. 18 the bundle of interzonal filaments is oblique to the radius of the 

 egg, though sometimes it varies only a little from that position. In 

 other cases it is very much bent, apparently as a result of a more rapid 

 ingrowth of the cell wall on one side during abstriction of the polar cell. 



